cache : add cache service (#457)

Signed-off-by: Bobby DeSimone <bobbydesimone@gmail.com>

internal/grpc/cache/client/cache_client.go

@@ -0,0 +1,57 @@
+package client
+
+import (
+	"context"
+
+	"github.com/pomerium/pomerium/internal/grpc/cache"
+	"github.com/pomerium/pomerium/internal/telemetry/trace"
+
+	"google.golang.org/grpc"
+)
+
+// Cacher specifies an interface for remote clients connecting to the cache service.
+type Cacher interface {
+	Get(ctx context.Context, key string) (keyExists bool, value []byte, err error)
+	Set(ctx context.Context, key string, value []byte) error
+	Close() error
+}
+
+// Client represents a gRPC cache service client.
+type Client struct {
+	conn   *grpc.ClientConn
+	client cache.CacheClient
+}
+
+// New returns a new gRPC cache service client.
+func New(conn *grpc.ClientConn) (p *Client) {
+	return &Client{conn: conn, client: cache.NewCacheClient(conn)}
+}
+
+// Get retrieves a value from the cache service.
+func (a *Client) Get(ctx context.Context, key string) (keyExists bool, value []byte, err error) {
+	ctx, span := trace.StartSpan(ctx, "grpc.cache.client.Get")
+	defer span.End()
+
+	response, err := a.client.Get(ctx, &cache.GetRequest{Key: key})
+	if err != nil {
+		return false, nil, err
+	}
+	return response.GetExists(), response.GetValue(), nil
+}
+
+// Set stores a key value pair in the cache service.
+func (a *Client) Set(ctx context.Context, key string, value []byte) error {
+	ctx, span := trace.StartSpan(ctx, "grpc.cache.client.Set")
+	defer span.End()
+
+	_, err := a.client.Set(ctx, &cache.SetRequest{Key: key, Value: value})
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// Close tears down the ClientConn and all underlying connections.
+func (a *Client) Close() error {
+	return a.conn.Close()
+}